Uniform discharge lamp



Patented July 9,1935

UNIFORM DISCHARGE LAMP ltobert Harding, Jr., Elmsi'ord, N. 'Y., assignor to Sirian Lamp Company, Newark, N. J., a corpo ration of Delaware Application November 17, 1930, Serial No. 496,142

Claims.

5 vice, Serial No.'459,048, filed June 3, 1930.

One of the objects of the invention is to provide 5m increased discharge area in a gaseous discharge Another object of the invention is to provide a lamp in which a discharge takes place between two elongated elements each of which is capable of maintaining its own independent discharge.

Another object of the invention is to provide an electric lamp in which a discharge takes place between two elements, the potential between opposite points on theelements always having substantially the same relation to the breakdown potential of the gas between said points.

Another object of the invention is to' provide an electric discharge lamp in which a pairof elements are spaced apart and a gaseous discharge is made to follow along each of the elements and to jump across the gap between them.

Other objects of the invention and objects relating to the method of constructing and assembling the various-parts will be apparent as the description of the'invention' proceeds.

One embodiment of the invention has been illustrated in the accompanying drawing in which:

Fig. 1 is a plan view of the elements ofmy imallel, the end of. one being connected to the opproved lamp; r

Fig. 2 is a sectional side elevation of the lamp;

and Fig. 3 is a front elevational view of the press and elements of the lamp.. 1

Referring no more specifically to the drawing, thelamp may comprise an envelope ill of glass or other transparent material formed integral with a press ll for.sea ling in the leading-in wires supporting the various parts of the lamp. A pair of elements l2 and i3 may be mounted spaced from each other and in substantially the same plane but each being curved with the convex sideof the curve adjacent the other. Each of the elements may comprise a coil it of resistance wire, such as tungsten, molybdenum, tantalum,

and nichrome, .or other resistance material which is closely wound in a concentrated coil and the "outer surfacefof the coil is coated with an elec-.

, tron'emitting material IS. The electron'emitting materiaimay be any'of the well knownoxides such as those of the alkaline earth metals includwing barium, strontium and calcium which-have an emissivity in excess of that of thorium oxide I or mixtures of any of these oxides and .should' perhaps contain some material, such as calcium oxide, capable of selective radiation when heated.

At each end of the coil I may provide a rod it, of tungsten or other metal capable of standing high temperature, whichextends-into the coil for a distance of two or three turns andto which the wires of the coil may be welded or the end of' the coil may extend outwardly to be welded to thesupport rod alongside of the rod Hi'. The electron emitting material is preferably extended over the ends of the coil so that itcovers a por-. tion of the rod IS. The rod l6 increases the conductivity of the ends of the element where the discharge may concentrate and prevents burning out.

The element l2 may have-its ends welded totwo support rods?" and I8 which may extend downwardly and inwardly to be sealed in the press I I, one at each end thereof. In like manner theelement I3 may have its ends welded to two supll adjacent the rods l1 and I8 respectively. The wire 19 may have a leading-in wire 2! connected to it and similarly the wire 20 may have a leading-in wire 22 connected to it. A wire 23 may be provided connecting the support rod l8 with the wire 2! while a wire 24 may be provided connecting the support rod I! with the wire 22. This construction places the two elements in parmaintain the" ionic discharge to the region of the elements i2 and H. For this purpose the pressure of about 200 mm; of mercury is sumcient. I prefer to use about 50 mm. of neon and 150 mm. of argon which produces a discharge giving an intense bluish-white light. The gases used should preferably be chemically pure or at least should not have an excess of one percent impurities. 1 I

It will be evident from an inspe'ction'of Fig. 1 that opposite points on the two filaments will 20 port rods l9 and 20 which may also extend downwardlyand inwardly and are sealed in the press have a difference in potential between-them as .thecorresponding ends of the elements are connected to opposite sides of the circuit. However if two opposite points 28 and 29 are chosenon the elements l2 and I3 respectively it will be evident that the potential difference between the two points is less than the potential difference between the ends of the elements where they join the support rods l1 and I 9 due to the resistance of the elements between the points 28 and 29 and their ends. Therefore, inasmuch as it is desired to have the relation between the potential difference of any two points on the elements and the breakdown potential of the gas between those points equal for any points on the elements, it is necessary to position these points closer together than the ends of the elements. It is for this reason that the elements are provided in curved form although if desired they may be bent at an angle with the vertices placed at the center and the sides extending away from each other.

With the elements positioned as indicated in the drawing and the envelope sealed onto the press the envelope may be connected in the usual manner to an exhaust pump andan oven may be placed over it to raise the temperature to somewhere in the neighborhood of 350 to 400 C. Current may also be run through the filaments to raise the temperature thereof to about 600 C. This heat is continued until a high vacuum of approximately .5 micron isobtained and all the gases have been removed from the envelope which is evidenced by no fluorescence when a high tension current from an induction coil is directed against the walls of the bulb. Current may then be increased through the filaments and the temperature thereof slowly raised until they are a bright red when the temperature will be about 800 C. This drives out any binder in theelectron emitting material and also certain occluded gases which have not'yet been removed. The

pump continues to remove from the envelope any gases which are driven out of the elements or other parts. v

When no more gas is found in the envelope the oven may be raised and the filaments heated to slightly less than 1200 Cato drive out any other occluded gases or'vapors which may be present.

The pump may then be shut ofi and a slight amount of an inert gas such as neon at a pres- 'spots appear it is an indication of other gases being present and the envelope should be exhausted again and the process repeated.

When the activation is completed the pump may again be connected to the envelope and the gas pumped out until the high vacuum is again produced. The filament circuit may then be disconnected and the pump turned off and about 50 mm. of neon gas admitted into the envelope followed'by about 150 mm. ofargon. The bulb may then be sealed off and is ready for use.

When the lamp is connected in a' circuit current flows through the wire 2| where it splits going to the support rod [9 and end of the filament I3 and also to the support rod l8 and op- P sit end of the filament l2. Current passes through the elements I! a:- d iii in the opposite direction and'leaves the element l3 by means of the support rod 20 and the element l2 by means of the support rod H which are both connected to the wire 22. Owing to the pressure of the gas in the bulb the discharge from the elements l2 and I3 is confined to the region adjacent the element insofar as the outer space between the elements and the envelope is concerned or the other parts, including the support rods, and a brilliant bluish-White discharge appears surrounding the elements like a halo. However inasmuch as opposite points on the elements have a difference of potential and inasmuch as this difference of potential is greater than the breakdown potential of the gas between the points the discharge will jump from one filament to the other. Owing to the fact that the relation between the breakdown potential of the gas between any two points on the elements and the potential difference between those two points is always the same the discharge between any two points on the elements will be the same and hence a uniform discharge will take place between the elements themselves somewhat as indicated by the dotted line in Fig. 1 whichwill produce an intense bluish-white illumination. When the filament is heated the emission of electrons therefrom apparently ionizes the gas in the vicinity of the filament and electrons appear to leave the surface of the filament and travel towards a point on the filament having a higher potential. Thus the breakdown potential of the gas per unit length of the filament is less than the potential across such unit length necessary to cause a current to fiow therein to raise the filament to operating electron emitting temperature. This must be true otherwise electrons would travel inside the filament. This relationbetween the breakdown potential of the gas and the current flowing in the filament is apparently only true in the vicinity of the filament, and if this were not so the discharge would probably fill the entire bulb instead of being restricted to the region of the filament.

If desired a metal vapor may be introduced into the bulb such as mercury, caesium, or rubidium vapor and various color effects may be obtained with the light by varying the gases and vapors used. Thus where a bluish-white light is desired as described above a predominance of argon may be used while if a red are discharge is desired a predominance of neon may be used; where a green light is desired mercury vapor may be used.

The metal vapor may be introduced into the envelope by providing a salt of the desired metal such as. mercuric, caesium, or rubidium chloride with magnesium in a small container 30 which may be secured to one of the support rods, such as l9, and may be provided with a pin hole out of which the metal vapor may pass when the container is subjected to sumcientheat, as by external bombardment after sealing oil, the

chloride dissociating into the chlorine and free metal. It may be desirable to use a small amount of caesium vapor with any of the above combinations as the caesium increases the conductivity of the gas and may produce a. much more brilliant light.

While two elements have been shown and deopposite points on any other elements bears to the breakdown potential between those points so that the discharge between the elements will always be uniform and of the same intensity.

.Note should be taken of the construction of the ends of the elements as indicated in Fig. 4 where a support rod extends inside of the coil of the resistance wire. The discharge surrounding the element narrows down at the end of the elementand might cause overheating at the end and burning out if this construction were not provided but where" the rod it enters the coil the resistance point is low and overheating is avoided even though the discharge concentrates or narrows down at this point. I

While the elements have been shown mounted in a horizontal plane perpendicular to the axis of the bulb it will be evident that they need not be mounted in the same plane at all and that they may be mounted vertically or in any other desired position as long as the proper spacing between the elements is maintained. Many modifications of the invention may be resorted to without departing from the spirit thereof, and I do not therefore desire to limit the invention to what has been shown and described except as such limitations occur in the I j appended claims.

What I desire to claim is: a 1 1. In an electric lamp a pair of conducting elements having an electron emissivity of the order of barium oxide connected in parallel with one end of one element connected to the opposite end of' the other element, said elements lying in substantially the same plane with the centers thereof nearer together than the ends thereof, and an inert ionizable gas surrounding said elements, the breakdown potential of said gas per unit length of one of said elements being less than the potential across saidunit length necessary to. maintain said element to electron emitting temperature within the normal operating potentials of said lamp.

2. In an electric lamp a pair of filament wires, a coating of material having high electron emission capacity comparable to that of barium oxide on each of said wires, said wires being substantially in the same plane and having substantially the same resistance, and being positioned so that the centers thereof are nearer together than the ends thereof, means to connect one end of each wire to the opposite end of the other, and an ionizable gas surrounding said elements, the breakdown potential of said gas per unit length of filament being less than the potential along said unit length of the filament necessary to maintain said filament at electron emitting temperature within the normal operating potentials of said lamp.

3. In an electric lamp a pair of arcuate conducting elements having a high electron emission capacity connected in parallel with one end of one element connected to the opposite end of the other element said elements being substantially in the same plane the centers nearer together than the ends, and a mixture of argon and neon gas surrounding said elements.

4. An electric lamp comprising an envelope, a coil of resistance wire bent in the form of an arc within said envelope, a coating of conducting material having a high'electron emission capacity on said coil, a second coil of resistance wire bent in the form of an arc and positioned with its convex side toward the convex side of the other coil, a coating of material having a high electron emission capacity on said second coil, said coils being connected together with one end of one coil connected to the opposite end of the other coil,

and a mixture of argon and neon gas within.

said envelope and surrounding said coils and having a pressure of approximately 200 mm. of

mercury.

5. In an electric lamp a pair of arcuate conducting elements having an'emissivity in excess of that from thorium oxide connected in parallel with one end of one element connected to the opposite end of the other element, and a mixture of gases of the argon group surrounding said elements.

ROBERT HARDING, JR. 

